Sierra International 18-0172 Oil Seal - Mercruiser 26-97530 The Sierra 18-0172 Oil Seal is interchangeable with the following: Mercruiser 26-97530. Each Sierra product meets or exceeds the original equipment part it replaces. Sierra Oil Seal OD: 1.500", Shaft Size: 0.845", Width: 0.315" Sierra part number: 18-0172 Interchangeable with the following: Mercruiser 26-97530